1. Field of the Invention
The present invention relates to a spin transistor, and more particularly, to a spin transistor that is conducive to the miniaturization and large scale integration of devices, because a magnetization direction of a source and a drain is determined by a direction of the epitaxial growth of a ferromagnet.
2. Description of the Related Art
Most integrated circuit technologies include devices manufactured utilizing metal oxide semiconductor field effect transistor (MOSFET) technology. In addition, memory devices such as a dynamic random access memory (DRAM), or flash memory, application-specific integrated circuits (ASIC) microprocessors, and logic circuits also operate based on an on/off operation of MOSFET.
In MOSFET, it is difficult to reduce the power consumption and area of the electronic device, and there is a physical limit on the gate oxide film. Among next-generation devices developed to solve the above-mentioned problems, there are devices to control the precession of electron spin using a voltage. Among these devices, a spin transistor includes a source, a drain, and a channel connecting the source and the drain. Here, the spin transistor is turned on/off under the control of the electron spin direction, and there have been attempts to use the spin transistor in switching devices, logic circuits, etc. The conventional semiconductor-based FET devices control the charge in the semiconductor using an electric field, but the spin transistor may control the charge and spin at the same time.
It was known that the previously proposed Datta-Das spin transistor (Applied physics letter, vol 56, 665, 1990) and its similar spin transistor disclosed in U.S. Pat. No. 5,654,566 entitled “Magnetic spin injected field effect transistor and method of operation” are required for injecting spin from a ferromagnet (a source) into a semiconductor, or from a semiconductor into a ferromagnet (a drain). Since ferromagnets (a source and a drain) determining a direction of electron spin in this spin injection are magnetized in a channel direction by using shape anisotropy, the ferromagnetic source and drain have a shape that is extended in a channel direction, and therefore the size (or, length) of the device is enlarged in the channel direction. Implementation of this earlier spin transistor in a large scale device has been difficult, and this spin transistor has problems (for example, low spin injection efficiency) caused by the heterogeneity in the interface of the semiconductor (a substrate) and the ferromagnets (a source and a drain).